This invention relates to a hydraulic cylinder cushion device for easing an impact at the end of a piston stroke.
When the piston rod of a hydraulic cylinder is fully extended, a cushion device which prevents impact of the piston on the cylinder acts to hydraulically brake the motion of the piston and reduce the speed of the piston at the end of the piston stroke.
When a cushion ring attached to the piston rod enters a circular cushion seal disposed in a bearing part of the cylinder in the vicinity of the end of the piston stroke, gaps formed therebetween form a throttle which resists oil flow, resists oil outflow from an oil chamber, increases the pressure of the oil chamber and hydraulically brakes the motion of the piston.
When the cushion ring enters the cushion seal, the cushion seal is pushed by fluid pressure so that it strikes a holder, and generates noise.
This is because, to facilitate the fitting between the cushion ring and cushion seal, the metal cushion seal disposed inside the holder is free to move slightly in the radial and axial direction of the piston rod.
As this striking noise is caused by metal coming together, it is a high frequency noise.
It is therefore an object of this invention to reduce this impact noise as much as possible.
It is another object of this invention to eliminate this impact noise by means of a simple construction.
In order to achieve above the objects this invention provides a cushion device for a hydraulic cylinder which comprises a piston slidably housed in a cylinder tube, a cylinder head through which a piston rod connected to the piston slidably penetrates, a cushion ring fixed to the piston rod, a cushion seal, the cushion seal being free to move within a certain range in the axial direction of the piston rod on the side of the cylinder head, and the cushion ring penetrating the inner circumference of the cushion seal in the vicinity of the end of the piston stroke, and restricting flow of fluid from an oil chamber in the cylinder tube to exert a cushion effect, and a spacer, the spacer being arranged on the inner side of the cushion seal in the axial direction and free to move by the same amount as the cushion seal, and its inner diameter being set larger than the inner diameter of the cushion seal.
The details as well as other features and advantages of the invention are set forth in the remainder of the specification and are shown in the accompanying drawings.